What must all communication cable bundles utilize when penetrating rated walls?

When communication cable bundles penetrate rated walls, they must utilize enclosed fire-rated pathway devices to maintain the integrity of the fire-resistive properties of the wall. These devices are specifically designed to seal the openings created by cable bundles and prevent the passage of fire, smoke, and toxic gases, which is critical in maintaining safety and compliance with building codes and fire safety regulations.

Enclosed fire-rated pathway devices not only protect the cables during a fire event but also ensure that the fire rating of the wall is not compromised. This is particularly important in commercial installations where adherence to safety standards is crucial. Employing these devices helps to prevent the spread of fire and smoke through penetrations, which could otherwise lead to significant hazards in case of an emergency.

The other options do not provide the same level of fire protection and compliance needed for rated wall penetrations. For example, while metal conduits are useful for protecting cables, they do not seal the penetration adequately to maintain the fire rating. Similarly, flexible conduits and bus ducts are not specifically designed to encapsulate cables in a way that preserves the wall's fire-resistive properties. Hence, the use of enclosed fire-rated pathway devices is the appropriate requirement in this scenario.